- The Washington Times - Wednesday, October 18, 2006

Colorblindness is a misnomer — seeing in only black and white is extremely rare. The more correct term would be color deficiency or color confusion.

“Colorblindness doesn’t mean you can’t see color at all,” says Dr. Roy Rubinfeld, a surgeon at Washington Eye Physicians and Surgeons in Chevy Chase. He is the clinical correspondent for the American Academy of Ophthalmology. “It varies from severe, or a problem with all colors, to very mild, where you can’t distinguish subtle differences in shades between two colors,” he says.

Total colorblindness is rare, as is blue-yellow deficit, or a difficulty in distinguishing between those two colors, local ophthalmologists say. Although colorblindness is an inherited trait, color vision loss can be the result of a brain tumor, stroke or disease, such as optic nerve disease or severe macular degeneration, they say.

More common is red-green deficit, a type of inherited colorblindness that affects 99 percent of those with colorblindness, says Julee Sylvester, spokeswoman for the Sight & Hearing Association, a nonprofit organization in St. Paul, Minn., dedicated to preventing sight and hearing loss.

“There is no treatment for colorblindness. It’s a matter of people learning how to compensate for not being able to distinguish colors,” Mrs. Sylvester says.

Colorblindness affects 7 percent of American males and 0.4 percent of females, Mrs. Sylvester says.

Colorblindness is not a condition that can be detected by an outsider, says Charles Ray Douglas, founder and president of the Color Blind Association, which was founded in Harlingen, Texas, in the early 1980s to test children for colorblindness.

“It doesn’t show. I’m not crippled. My face isn’t distorted,” says Mr. Douglas, who has red-green deficit and has two grandsons who are colorblind. “People don’t understand why I can’t see red, green and brown.”

Mr. Douglas says differentiating among the three colors is difficult and confusing for him.

“That’s why confusion is a better term than blindness. I’m not blind. I have perfect vision, even at 77,” he says.

Mr. Douglas, who holds a doctorate in genetics, says he learned how to use a process of elimination and guess at some of the colors he was supposed to see.

“We do OK with traffic signals. The green signal has a little blue in it, so we pick up on the blue,” he says, adding that it helps that the green light on most traffic signals is located on the bottom or right.

Red-green colorblindness is carried on the sex-linked X chromosome and is a recessive trait, Dr. Rubinfeld says. Males have one X and one Y chromosome and females two X chromosomes, so for females to be colorblind, they must inherit the gene on both chromosomes and men on only the X chromosome, he says.

Red-green colorblindness is passed on through the mother, who either is colorblind or is a carrier, Mr. Douglas says.

“Males have one chance to get a good gene,” he adds.

Problems with seeing color occur in the eyes, which send a message to the brain that is inaccurate or lacks color information, Dr. Rubinfeld says. The retina, the lining in the back of the eye, has two types of photoreceptor cells, the rods and cones, which are able to detect light energy, he says. The rods help with night vision and seeing black and white, while the cones help with perceiving color, he says.

“From the retina, there is a large nerve called the optic nerve that takes visual information and sends it to the brain. The brain makes sense of it and turns it into images and vision,” Dr. Rubinfeld says.

The cones contain pigments sensitive to the three wavelengths of visible light, which are red, green and blue, and decrease in size in that order, says Dr. Maxwell Helfgott, chairman of the ophthalmology department at the Washington National Eye Center of the Washington Hospital Center in Northwest. When light from one of the wavelengths hits the retina, it causes the cone sensitive to that particular wavelength to fire, unless the cone is missing or defective, he says.

“It’s only working with intensity of light rather than specific information of what wavelength of light it is,” Mr. Helfgott says.

For example, if the red cone is missing and light is coming from a red object, the retina may not be able to identify the color, or the value of the color will be diminished, he says.

The cones for each color are triggered by a particular wavelength, says Sarah Tishkoff, associate professor of biology at the University of Maryland in College Park.

“Different colors emit light at different wavelengths,” says Ms. Tishkoff, who holds a doctorate in human genetics. “Higher processing in the brain will distinguish the different colors.”

The genes, which contain the coding instructions for the light-sensitive pigments, are carried on the X chromosome for the green and red pigments, Ms. Tishkoff says. The blue pigment is believed to be on a different, non-sex-linked chromosome, she says.

Colorblindness is diagnosed through clinical testing. The most common tests are the Ishihara Tests for Color-Deficiency, which consist of a series of diagrams with colored dots that disguise numbers made up of red, green and other colors of dots.

“If you can’t see the numbers, that means those are the colors you can’t perceive,” Dr. Rubinfeld says. “You can break down the type of colorblindness you have by which numbers you can see and can’t see.”

Colorblindness is not life-threatening and does not affect a person’s health, he says. It can, however, prevent or make difficult entry into certain fields, such as being a pilot, police officer, designer or someone who works with color. It also can affect skills in matching clothes and colors.

“Some people, since they’re born with it, don’t perceive it as a problem. You show them different colors, they see variations, depening on what type of colorblindness they have,” says Dr. Benjamin Osborne, neuro-ophthalmologist at Georgetown University Hospital in Northwest. “It’s usually a pretty benign condition. It doesn’t cause significant limitations on daily living.”

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